1. Field of the Invention
The present invention is directed toward a luminaire and particularly to a luminaire fixture carrying a monochromatic light source disposed before a reflector for transmitting light through a configured multilayer interference mirror to produce a controlled light pattern.
2. Description of Other Art
Over the past few years, designers in the lighting industry have become concerned over the amount of energy used in a luminaire to provide a required amount of light. The amount of light required for any particular use has been generally set forth in the Illuminating Engineering Society (IES) Lighting Handbook, Fifth Edition, 1972. One particular use is the illumination of relatively even surfaces, as in roadway lighting and parking area lighting. It is important in illuminating these areas that sufficient illumination be provided to aid in preventing accidents and crime and in providing convenience and comfort.
Recently, however, designers in the lighting industry have become increasingly aware of conserving energy in the field of outdoor lighting. Luminaires that fulfill the lighting requirements of the IES are becoming unmarketable because of the expensive energy demands of the luminaires. At least one designer has approached this problem by suggesting a change in the light source used in the luminaire to "lend themselves to sophisticated reflector/refractor optical systems" Lighting Design & Application, "HPS and LPS--a primer", Terry K. McGowan, pp. 19-23, December, 1974. This designer states that lighting from luminaires with low pressure sodium (LPS) lamps is less efficient than lighting from luminaires with high pressure sodium (HPS) lamps because too much light emitted from the luminaires with LPS lamps misses or is misdirected to other than the task area. Accordingly, even though LPS lamps may under controlled circumstances be considered to have greater efficiency than HPS lamps, luminaires with HPS lamps are used because of a greater control over the light distribution pattern.
In before mentioned U.S. Pat. Application Entitled "A Luminaire Using a Multilayer Interference Mirror", Ser. No. 821,129 for inventors T. W. Dry and E. C. Letter which is a continuation-in-part of Ser. No. 716,409, there is described a luminaire incorporating the use of a directionally sensitive interference coating to achieve the directional control of monochromatic light in a luminaire by utilizing such a coating in cooperation with established conventional configured components of luminaires representative of the state of the art.
A luminaire is considered to be a lighting fixture used either for roadway lighting or for interior or exterior lighting. A luminaire assembly includes a monochromatic light source. Monochromatic light sources generally are defined as sources which emit luminous flux 75% of which falls within a bandwidth of 40 nanometers. Such monochromatic light sources include low pressure sodium lamps, light emitting diodes, neon lamps and lasers.
In the invention of the aforementioned patent continuation-in-part application Ser. No. 821,129, there is described a coating which predominantly transmits the light which is incident within a certain range of angles, and predominantly reflects light incident outside of that range. The luminaire proposed by that invention is comprised of a monochromatic source, which is preferably a low pressure sodium (LPS) lamp, diffuse reflector and a coated plate. The coating is selected to predominantly transmit light rays incident between 25.degree. and 60.degree. to essentially 90.degree., depending upon the efficiency application. These rays escape the luminaire and pass into the predetermined range characteristic of the coating.
Such a luminaire will distribute light from a large monochromatic source, such as an LPS lamp into, for example, a "radial batwing" considered desirable principally for the illumination of large planar areas such as parking lots, warehouses, parks and recreational fields. Such a pattern results in the illumination of the largest possible area with relative uniformity and minimum glare.
The directional sensitivity principle has been further developed in order to be more useful in roadway lighting. Because of its exceedingly superior light production as compared with other light sources, the LPS source is a desirable element for roadway lighting where very large areas must be illuminated at minimum energy consumption. Although superior, the large size of the LPS source, necessary for providing sufficient illumination, has made luminaire design difficult. Luminaires with LPS lamps, using classical reflection and refraction to control the light distribution, inherently allow far too much light to miss the roadway or target illuminated area. Some light falls to the near and far side of the roadway and some even leaves the luminaire in an upward direction, causing glare and loss of light. As a result, such luminaires have a low coefficient of utilization. The coefficient of utilization is a standard term adopted by the Illuminating Engineering Society to denote the proportion of light which falls onto the desired task area. The term is defined in the IES Lighting Handbook, Fifth Edition, 1972, as the ratio of the luminous flux (lumens) from a luminaire received on the work plane to the lumens emitted by the luminaire's lamps alone. To date, the low coefficient of utilization of LPS luminaires for roadway lighting has prevented such a potentially useful source from being acceptable for use within a roadway luminaire in the United States and some other countries.